Codes and barn conversions

I've got some clients that want to convert a 1830's threasing barn into a home. I know they are going to ask about what it will take to satisfy code enforcement. How do you verify the strength of old timbers ? Are there any models that could be refered to the powers that be so as to make them happy that your building won't fall down.

Timbo,

By my calculations the barn has been standing for 170+ years. That would seem to prove it's strength.
It would appear your job is to convince them what you are doing to it during the adaptive re-use conversion work won't weaken it.

Rudy